In recent years, in an image reading apparatus, such as a personal facsimile, small light emitting diodes (hereinafter referred to as an LED) with a low power are starting to be used as a light source of a reading light source apparatus, due to improvements in an output of such LEDs and a raise in the sensitivity of a CCD type sensor as a light receiving element. In a conventional linear light source apparatus equipped with such LEDs as light sources, the number of the light sources is reduced and a light guiding member in which light emitted from the light source enters the light guiding member and the light is guided towards a desired direction, is used so as to obtain uniform lighting intensity.
FIG. 8 is a diagram showing the structure of a linear light source apparatus disclosed in Japanese Laid Open Patent No. H09-163080 as a conventional linear light source apparatus. The linear light source apparatus is equipped with a light guiding member 1 which is made of transparent resin etc., and a light source 2 which is made up of LEDs. A light receiving section 3 is formed at one end of the light guiding member 1 in an axial direction thereof, and a flat and smooth face 4, on which a reflective film is formed, is provided at the other end thereof. The light source 2 is arranged so as to face the light receiving section 3. Moreover, knurled recess portion 5 is formed so as to extend in the axial direction on an outer circumferential surface of the light guiding member 1 which is in an opposite side to a light emission side of the light guiding member 1. The cut-out direction of recesses of the knurled recess portion 5 is perpendicular to the axial direction. The recesses are in a shape of isosceles triangle in a cross sectional view thereof, taken along in the axial direction. Light emitted from the light source 2 enters the inside of the light guiding member 1 from the light receiving section 3, and the light is repeatedly reflected within the light guiding member 1, and is then reflected on reflective surfaces 6 of the knurled recesses 5, so as to be emitted from the light guiding member 1 with predetermined angles.
Of components of light emitted from the light source 2, a light ray al of the light with a large incident angle to the light receiving section 3 is reflected on a reflective surface 6 of one of the knurled recesses 5 near the light receiving section 3 (a light ray α2). Since the light ray α1 with the large incident angle to the light receiving section 3, is incident on the reflective surface 6 of the recess of the knurled recess portion 5 at a small incident angle (the light ray α2), a light ray α3 is emitted from the light guiding member 1 at an output angle which is approximately perpendicular thereto (slightly inclining in the direction of the flat and smooth face 4). On the other hand, of the components of the light emitted from the light source 2, a light ray β1 whose incident angle with respect to the light receiving section 3 is small, propagates along the axial direction of the light guiding member 1, and is reflected on a reflective surface 6 of another recess of the knurled recess portion 5 which is distant from the light receiving section 3 and near the flat and smooth face 4 (a light ray β2). Since the light ray β1 with the small incident angle with respect to the light receiving section 3 is incident on the reflective surface 6 of the recess of the knurled recess portion 5 at a large incident angle (a light ray β2), a light β3 is emitted from the light guiding member 1 with an angle, inclining in a direction of the flat and smooth face 4.
However, in the linear light source apparatus shown in FIG. 8, since the light β3 is outputted at an angle, inclining in the direction of the flat and smooth face 4, a black line may appear in a scanned image. FIG. 9 is a partial cross sectional view of the image reading apparatus, wherein an object 42 to be scanned and light rays are shown for explanation of a shadow 44. A platen glass 41, which is made of an optical permeability material, is provided in the image reading apparatus so as to face a light emitting face 9 of the linear light source apparatus. The reading object 42 to be scanned, which has an image thereon, is placed on the platen glass 41, when it is used. Light emitted from the light emitting face 9 of the light guiding member 1 is irradiated to the platen glass 41, so that a projection image of the reading object 42 is scanned, so as to form a reading image. When the reading object 42 having a thickness such as a book etc. is scanned, a gap is produced between a face of the reading object 42 to be irradiated, and a document cover 43. Since the reading object 42 does not transmit light, a light ray β3a which irradiates an end portion of the reading object 42 does not irradiate the document cover 43. Although the light ray β3b which is slightly shifted in the axial direction from the light ray β3a which irradiates the end portion of the reading object 42, irradiates the document cover 43, since the light β3b has an angle, a portion to be irradiated thereby is shifted in the axial direction from the edge of the reading object 42, that is, the document cover 43 is irradiated. Therefore, a shadow 44 is produced between the light β3a and the light β3b, since the light is not irradiated there, so that a black line appears in a reading image. Moreover, a similar thing happens when there is difference in level such as a folded line, in the reading object 42.
In view of the problem, the present light guiding member and a linear light source apparatus emit light so that a black line may not appear in a reading image, even when there is a gap or a level difference in a reading object.
One of aspects thereof is a light guiding member in a shape of a rod shape comprising: a light receiving portion formed on an end thereof in an axial direction thereof; and a knurled recess portion which extends in the axial direction, is formed on a side face thereof, wherein the knurled recess portion has two or more recesses, a side face of each recess in a light receiving portion side is a reflective surface, and the reflective surface of at least one of the recesses having a primary reflective surface and a secondary reflective surface.
The secondary reflective surface may be formed at an end of the primary reflective surface in the axial direction, and an inclination angle of the secondary reflective surface may be larger than that of the primary reflective surface.
Further, at least one of the recesses may have a reflective surface, a flat surface and a light transmissive face, and the light transmissive face may comprise a primary light transmissive face and a secondary light transmissive face.
Moreover, the primary light transmissive face may be formed at an end of the secondary light transmissive face, and an inclination angle of the secondary transmissive face may be larger than that of the primary light transmissive face.
Moreover, at least one of the recesses may have a reflective surface, a flat surface and a light transmissive face, and the flat surface may incline counterclockwise from the axial direction.
Widths of flat faces in the axial direction may be shorter as away from the light receiving portion to the flat and smooth face.
Depths of the recesses are larger as close to the flat and smooth face from the light receiving portion.
One of the two or more recesses of the knurled recess portion may have a one face reflective surface made up of one face, and another one of the two or more recesses of the knurled recess portion may have a two face reflective surface made up of a primary reflective surface and a secondary reflective surface.
The one of the two or more recesses of the knurled recess portion which has the one face reflective surface, and the another one of the two or more recesses of the knurled recess portion which has the two face reflective surface made may be formed by turns.
Another aspect of the present light guiding member and a linear light source apparatus is a liner light source apparatus comprising: the above-mentioned light guiding member; and a light source provided so as to face the light receiving portion of the light guiding member.
In the present light guiding member and the linear light source apparatus, since the reflective surface of the recess of the knurled recess portion has the primary reflective surface and the secondary reflective surface, the light rays having two angles which are different in the axial direction can be directed to a reading object and emitted from the linear light source apparatus, so that even when there is a gap or a level difference in a reading object, a shadow is not produced on the document cover, whereby a black line does not appear in the reading image.